At present, in many application scenarios, azimuth or distance information needs to be provided, and the azimuth or distance information is applied to emergency communications, road mapping or some military missions.
In the prior art, a fundamental principle of a global positioning system (Global Positioning System, GPS) is to measure a distance between a satellite with a known position and a receiver of a user, and then a specific position of the user can be known by combining data of a plurality of satellites. A distance between the user and the satellite is obtained by recording time for a satellite signal to be transmitted to the user, and then multiplying the time by propagation speed of an electromagnetic wave.
When a GPS satellite works normally, the GPS satellite continuously uses a pseudo-random code (pseudo code for short) formed by binary code elements 1 and 0 to transmit a navigation message. The navigation message includes information such as satellite ephemeris, working condition, clock correction, ionospheric delay correction and atmospheric refraction correction. The navigation message is obtained by demodulating a satellite signal, and is modulated at 50 b/s on a carrier frequency for transmission. Each main frame of the navigation message includes 5 subframes, and a length of each subframe is 6 s. Each of first three frames has 10 character codes, which are repeated every 30 seconds and updated once per hour. Last two frames are 15000 b in total. When receiving a navigation message, the user extracts satellite time and compares the satellite time with the user's own clock to know a distance between a satellite and the user, and then uses satellite ephemeris data in the navigation message to calculate a position where the satellite is located when transmitting the message, so information such as position and speed of the user in a geodetic coordinate system can be known.
However, in practical applications, some problems exist in a civilian GPS system. For example, when a GPS technology is adopted to calculate a distance between a satellite with a known position and a user, after time is determined, speed is the propagation speed of the electromagnetic wave, but in a propagation process of the electromagnetic wave in the atmosphere, a signal is susceptible to interference in the ionosphere and the troposphere, so the GPS system can only perform average calculation on the signal, which causes low precision in distance calculation.